X-ray cassettes in the past have been composed of a rectangular body with a cover hinged to the body and a pair of intensifying sheets retained therein to interpose therebetween an X-ray film. A cushion pad is interposed between the cover and one intensifying sheet attached to the cover so as to press the intensifying sheet against the X-ray film. The cushion pad may be of sponge rubber, resilient foam, felt, or a cushion of elastic sheet material as disclosed in U.S. Pat. Nos. 2,359,522; 3,466,440; 3,482,097 and 3,964,107 respectfully. The rectangular shaped cover has hinge means on its rear edge and latch means on its sides. The hinge means have been composed of a pair of hinges to pivotally mount the cover at one side thereof to the body, and the latch means secure the cover to the cassette rectangular body.
The above described conventional X-ray film cassette has a defect in that the central portion of the cover is not sufficiently pressed against the body and accordingly the central portion of the intensifying sheet is not in perfect contact with the X-ray film. Therefore, uniformly sharp radiographic images are difficult to obtain with the conventional X-ray film cassette.
An improvement to these cassettes has been disclosed in U.S. Pat. No. 4,032,790 which provides a convexed resilient cover working in conjunction with a perforated resilient pad to provide better contact between the intensifying screens and the X-ray film. This improvement has a draw back, however, in that there is no interconnection between the perforated holes of the pad and therefore air can be trapped causing unequal contact between the intensifying screens and the X-ray film resulting in light and dark spots in the developed X-ray film.
The object of the present invention is to solve this air trap problem in order to obtain sharp radiographic images on the developed X-ray film.